Obesity in the elderly can be masked by body composition changes that result in a net weight loss. Sarcopenia, the loss of muscle and function with age, is universal in the elderly. The reduced protein stores inherent in sarcopenia leave the elderly with decreased ability to cope with illness or injury. The combination of increased %fat and sarcopenia results in a body composition status described as "sarcopenic obesity". This condition cannot be assessed by anthropometry or other traditional indirect body composition methods. The purpose of the proposed research is to develop and test a portable and relatively inexpensive instrument (X-ray absorptiometer) for carrying out body composition analysis of soft tissue in the field. These measurements are important for providing an index of nutritional status of individuals and will be used to evaluate the benefits and risks of anabolic treatments, nutritional support and the management of obesity in children and adults. Being portable, inexpensive, and simple to use, the instrument will permit the evaluation of nutritional health status of individuals in their own environment. It will be particularly beneficial to those for whom access to hospitals is difficult or limited (e.g. elderly in nursing homes or assisted living) or in underdeveloped nations, where aggressive nutrition support programs are being evaluated. The design is based on single and dual energy X-ray absorptiometry (DXA), optimized for soft tissue. The instrument is a hand-held caliper with a collimated X-ray source and a detector. The use of a simple detector array will facilitate the positioning of the caliper. The instrument will be evaluated for both single and dual energy mode and will be tested against mid-thigh CT and reference whole body composition techniques. The outcome of this research will be a fully developed and tested instrument and a method for its use in the field. This portable instrument will be particularly useful for monitoring sarcopenic obesity in the elderly where existing simple methods (such as Body Mass Index) fail to identify the true level of adipose tissue and frailty.